Adds optional TCP_KEEPALIVE to WebSocketServer

TCP_KEEPALIVE is now enabled by default. Settings for
KEEPCNT, KEEPINTVL and KEEPIDLE can be supplied when
creating WebSocketServer and KEEPALIVE can also be
disabled if required.

Also adds new unit test for testing.

Co-authored-by: natsume.takashi@lab.ntt.co.jp
Fix search path construction in tests.

This way the tests can be run directly from within the tests directory
and they might also have a chance of running on Windows (where the
path separator is different).
Merge pull request #93 from dosaboy/topic/set-keepalive-options

Adds optional TCP_KEEPALIVE to WebSocketServer
Added unit tests for websocket and websocketproxy

To run the unit tests just run tox from the top
level directory which will try to run unit tests
for most versions of python. Requires tox to be
installed. To run tox for a specifice env, run
tox -e<env> e.g. for python 2.7 run 'tox -epy27'.

Co-authored-by: natsume.takashi@lab.ntt.co.jp
Merge pull request #94 from dosaboy/topic/add-unit-tests

Added unit tests for websocket and websocketproxy